I. Field of the Invention
The present technology relates to: (i) a cleaning device which is provided in an image forming apparatus adopting an electrophotographic system and which removes residual toner by bringing a blade into contact with a surface of an image carrier such as a photoreceptor drum; and (ii) an image forming apparatus including the cleaning device. More specifically, the present technology relates to a cleaning device more suitable for use in an image forming apparatus in which an image carrier is charged by using a contact charging system.
II. Related Art and other Considerations
According to an electrophotographic system adopted by an image forming apparatus such as a copier or a laser printer, the following operations are carried out. Specifically, a surface of a photoreceptor serving as an image carrier is charged by a charging device. Thereafter, an electrostatic latent image is formed by carrying out an exposure with the use of an exposure device, and a toner image is formed by developing the electrostatic latent image with the use of a developing device. Then, the toner image is electrostatically transferred, for example, onto a paper sheet (transferring medium), by a transferring device. Thereafter, the toner image thus transferred onto the paper sheet is fixed by a fixing device. Thus, an image is formed on the paper sheet.
The charging device is mainly classified into two types: (i) a contact-charging-type charging device using a charging roller, a charging brush, or other member; and (ii) a noncontact-charging-type charging device typified by corona charging. Among these, the contact-charging-type charging device brings a charging member such as a roller or a brush into direct contact with a photoreceptor so as to cause electrons to adhere to the photoreceptor. Therefore, the contact-charging-type charging device has the following advantages (1) to (3): (1) charging can be carried out efficiently; (2) a low voltage can be applied to the charging member; and (3) only a very small amount of ozone, which is a cause of environmental pollution, is generated.
Further provided around the photoreceptor is a cleaning device for removing toner remaining on the photoreceptor. Because of space-saving, design simplicity, mechanism simplicity, and/or other reason, a cleaning device that is frequently used today uses a blade (cleaning blade) that scrapes toner by making contact with a surface of a photoreceptor.
Further, for the purpose of realizing an image with high resolution, a high-speed machine and a color machine, which have been a recent mainstream type of electrophotographic image forming apparatus, start to use toner (small-particle toner) having a small particle diameter of approximately 5 μm. Among other small-particle toner, shape-controlled toner is widely used which is produced, for example, by a polymerization method in consideration of a cleaning property.
The blade carries out toner cleaning as follows. Force is applied, in a direction parallel to a surface of a photoreceptor, to toner adhering to the surface of the photoreceptor by electrostatic force (coulomb force) and mechanical force (van der Waals' force). The toner slides along the photoreceptor so as to be removed. On this occasion, since spherical toner with no corner has a larger contact area with respect to the surface of the photoreceptor than that of toner with a corner and without regular shape, a great frictional force is exerted. This causes the spherical toner with no corner to have a difficulty of sliding along the photoreceptor. Instead, it is easy for the spherical toner to roll. As a result, the spherical toner rolls in a space between the photoreceptor and the cleaning blade, and so scrapes through the cleaning blade. This makes it difficult to carry out cleaning. Only a small effect is brought about simply by increasing the line pressure of the blade. Instead, the abrasion of the photoreceptor is accelerated, so that the photoreceptor has a short life span.
The following describes examples of conventional techniques for solving such problems.
According to Japanese Unexamined Patent Publication No. 58009/2003 (Tokukai 2003/58009; published on Feb. 28, 2003), a lubricant agent such as zinc stearate is applied to a surface of a photoreceptor with the use of a cleaning blade, so that the coefficient of sliding friction of toner is reduced. In this case, the cleaning blade is set to have a rebound resilience of 45% to 65% and a line pressure of 0.2 N/cm to 0.5 N/cm.
Further, according to Japanese Unexamined Patent Application No. 267535/2000 (Tokukai 2000-267535; published on Sep. 29, 2000, a cleaning blade is set so as to have a JIS A hardness of 70° to 80° and a rebound resilience of 20% to 40%.
According to Japanese Unexamined Patent Application No. 98925/2003 (Tokukai 2003/98925; published on Apr. 4, 2003), a photoreceptor 1 has a surface layer that contains siloxane resin, and a cleaning blade is set so as to have a rebound resilience of 5% to 30% at 30° C. and a rebound resilience of 10% to 40% at 40° C.
However, in cases where small-particle toner with no corner is used, the arrangements respectively described in Tokukai 2003-58009, Tokukai 2000-267535, and Tokukai 2003-98925 suffer from the following problems (1) to (4): (1) the photoreceptor cannot be charged uniformly; (2) a cleaning property is low; (3) the photoreceptor has a short life span; and/or (4) the original electrophotographic performance of the photoreceptor is degraded.
According to the arrangement of Tokukai 2003-58009, although the lubricant agent is applied to the surface of the photoreceptor because the blade has a rebound resilience of 45% to 65%, the blade is caused to make contact with the spherical toner at a high line pressure and a high modulus. For this reason, the photoreceptor is easily worn away due to friction with the blade. This causes the photoreceptor to have a short life span. In addition, in cases where the blade having such a high rebound resilience of 45% to 65% is used, for example, in a high-speed machine operating at a processing speed of 300 mm/sec, the amplitude of a stick-slip motion is so high that the toner easily passes through a space between the photoreceptor and the blade. This causes a cleaning property to be reduced. The stick-slip motion will be described later.
Further, since the lubricant agent is applied by a brush or the like, the surface of the photoreceptor is made uneven by fine particles of the lubricant agent. However, the blade having a rebound resilience of 45% to 65% cannot make the unevenness even because the edge portion of the blade is pressed against the photoreceptor but is little squashed. Therefore, the unevenness on the surface of the photoreceptor easily causes uneven charging, and causes a charge leak especially when the cleaning device is combined with a contact-charging-type charging device.
Further, according to Tokukai 2000-267535, the properties of the blade are defined in accordance with (i) the circumferential velocity of the photoreceptor, (ii) the resin contained in the toner, and (iii) the average particle diameter of the toner. However, small-particle toner with no corner has a problem with a cleaning property.
Further, according to Tokukai 2003-98925, the surface layer of the photoreceptor contains siloxane resin for the purpose of ensuring a high cleaning property. However, this degrades the original electrophotographic performance of the photoreceptor.